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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-13 == Outdated reference: A later version (-13) exists of draft-ietf-detnet-architecture-04 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL P. Thubert, Ed. 3 Internet-Draft Cisco 4 Intended status: Standards Track R. Jadhav, Ed. 5 Expires: September 20, 2018 Huawei Tech 6 J. Pylakutty 7 Cisco 8 March 19, 2018 10 Root initiated routing state in RPL 11 draft-ietf-roll-dao-projection-03 13 Abstract 15 This document proposes a protocol extension to RPL that enables to 16 install a limited amount of centrally-computed routes in a RPL graph, 17 enabling loose source routing down a non-storing mode DODAG, or 18 transversal routes inside the DODAG. As opposed to the classical 19 route injection in RPL that are injected by the end devices, this 20 draft enables the root of the DODAG to projects the routes that are 21 needed on the nodes where they should be installed. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on September 20, 2018. 40 Copyright Notice 42 Copyright (c) 2018 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. New RPL Control Message Options . . . . . . . . . . . . . . . 3 60 3.1. Via Information Option . . . . . . . . . . . . . . . . . 4 61 4. Projected DAO . . . . . . . . . . . . . . . . . . . . . . . . 5 62 4.1. Non-storing Mode Projected DAO . . . . . . . . . . . . . 6 63 4.2. Storing-Mode Projected DAO . . . . . . . . . . . . . . . 8 64 5. Applications . . . . . . . . . . . . . . . . . . . . . . . . 10 65 5.1. Loose Source Routing in Non-storing Mode . . . . . . . . 10 66 5.2. Transversal Routes in storing and non-storing modes . . . 11 67 6. RPL Instances . . . . . . . . . . . . . . . . . . . . . . . . 13 68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 69 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 70 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 71 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 72 10.1. Normative References . . . . . . . . . . . . . . . . . . 15 73 10.2. Informative References . . . . . . . . . . . . . . . . . 15 74 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 16 75 A.1. Using storing mode P-DAO in non-storing mode MOP . . . . 16 76 A.2. Projecting a storing-mode transversal route . . . . . . . 17 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 79 1. Introduction 81 The "Routing Protocol for Low Power and Lossy Networks" [RFC6550] 82 (LLN)(RPL) is a generic Distance Vector protocol that is well suited 83 for application in a variety of low energy Internet of Things (IoT) 84 networks. RPL forms Destination Oriented Directed Acyclic Graphs 85 (DODAGs) in which the root often acts as the Border Router to connect 86 the RPL domain to the Internet. The root is responsible to select 87 the RPL Instance that is used to forward a packet coming from the 88 Internet into the RPL domain and set the related RPL information in 89 the packets. 91 The 6TiSCH architecture [I-D.ietf-6tisch-architecture] leverages RPL 92 for its routing operation and considers the Deterministic Networking 93 Architecture [I-D.ietf-detnet-architecture] as one possible model 94 whereby the device resources and capabilities are exposed to an 95 external controller which installs routing states into the network 96 based on some objective functions that reside in that external 97 entity. 99 Based on heuristics of usage, path length, and knowledge of device 100 capacity and available resources such as battery levels and 101 reservable buffers, a Path Computation Element ([PCE]) with a global 102 visibility on the system could install additional P2P routes that are 103 more optimized for the current needs as expressed by the objective 104 function. 106 This draft enables a RPL root, with optionally the assistance of a 107 PCE, to install and maintain additional storing and non-storing mode 108 routes within the RPL domain, along a selected set of nodes and for a 109 selected duration, thus providing routes more suitable than those 110 obtained with the distributed operation of RPL. Those routes may be 111 installed in either storing and non-storing modes RPL instances, 112 resulting in potentially hybrid situations where the mode of the 113 projected routes is different from that of the other routes in the 114 instance. 116 2. Terminology 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 120 document are to be interpreted as described in [RFC2119]. 122 The Terminology used in this document is consistent with and 123 incorporates that described in "Terminology in Low power And Lossy 124 Networks"[RFC7102] and [RFC6550]. 126 3. New RPL Control Message Options 128 Section 6.7 of RPL [RFC6550] specifies Control Message Options (CMO) 129 to be placed in RPL messages such as the Destination Advertisement 130 Object (DAO) message. The RPL Target Option and the Transit 131 Information Option (TIO) are such options; the former indicates a 132 node to be reached and the latter specifies a parent that can be used 133 to reach that node. Options may be factorized; one or more 134 contiguous TIOs apply to the one or more contiguous Target options 135 that immediately precede the TIOs in the RPL message. 137 This specification introduces a new Control Message Option, the Via 138 Information option (VIO). Like the TIO, the VIO MUST be preceded by 139 one or more RPL Target options to which it applies. Unlike the TIO, 140 the VIO are not factorized: multiple contiguous Via options indicate 141 an ordered sequence of routers to reach the target(s), presented in 142 the order of the packet stream, source to destination, and in which a 143 routing state must be installed. 145 The Via Information option MUST contain at least one Via Address. 147 3.1. Via Information Option 149 The Via Information option MAY be present in DAO messages, and its 150 format is as follows: 152 0 1 2 3 153 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 | Type = 0x0A | Option Length | Path Sequence | Path Lifetime | 156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 157 | | 158 + + 159 . . 160 . Via Address 1 . 161 . . 162 + + 163 | | 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | | 166 . .... . 167 | | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | | 170 + + 171 . . 172 . Via Address n . 173 . . 174 + + 175 | | 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 178 Figure 1: Via Information option format 180 Option Type: 0x0A (to be confirmed by IANA) 182 Option Length: In bytes; variable, depending on the number of Via 183 Addresses. 185 Path Sequence: 8-bit unsigned integer. When a RPL Target option is 186 issued by the root of the DODAG (i.e. in a DAO message), that 187 root sets the Path Sequence and increments the Path Sequence 188 each time it issues a RPL Target option with updated 189 information. The indicated sequence deprecates any state for a 190 given Target that was learned from a previous sequence and adds 191 to any state that was learned for that sequence. 193 Path Lifetime: 8-bit unsigned integer. The length of time in 194 Lifetime Units (obtained from the Configuration option) that 195 the prefix is valid for route determination. The period starts 196 when a new Path Sequence is seen. A value of all one bits 197 (0xFF) represents infinity. A value of all zero bits (0x00) 198 indicates a loss of reachability. A DAO message that contains 199 a Via Information option with a Path Lifetime of 0x00 for a 200 Target is referred as a No-Path (for that Target) in this 201 document. 203 Via Address: 16 bytes. IPv6 Address of the next hop towards the 204 destination(s) indicated in the target option that immediately 205 precede the VIO. TBD: See how the /64 prefix can be elided if 206 it is the same as that of (all of) the target(s). In that 207 case, the Next-Hop Address could be expressed as the 8-bytes 208 suffix only, otherwise it is expressed as 16 bytes, at least in 209 storing mode. 211 4. Projected DAO 213 This draft adds a capability to RPL whereby the root projects a route 214 through an extended DAO message called a Projected-DAO (P-DAO) to an 215 arbitrary router down the DODAG, indicating a next hop or a sequence 216 of routers via which a certain destination indicated in the Target 217 Information option may be reached. 219 A P-DAO message MUST contain at least a Target Information option and 220 at least one VIA Information option following it. 222 Like a classical DAO message, a P-DAO is processed only if it is 223 "new" per section 9.2.2. "Generation of DAO Messages" of the RPL 224 specification [RFC6550]; this is determined using the Path Sequence 225 information from the VIO as opposed to a TIO. Also, a Path Lifetime 226 of 0 in a VIO indicates that a route is to be removed. 228 There are two kinds of P-DAO, the storing mode and the non-storing 229 mode ones. 231 The non-storing mode P-DAO discussed in section Section 4.1 has a 232 single VIO with one or more Via Addresses in it, the list of Via 233 Addresses indicating the source-routed path to the target to be 234 installed in the router that receives the message, which replies 235 to the root directly with a DAO-ACK message. 237 The storing mode P-DAO discussed in section Section 4.2 has at 238 least two Via Information options with one Via Address each, for 239 the ingress and the egress of the path, and more if there are 240 intermediate routers. The Via Addresses indicate the routers in 241 which the routing state to the target have to be installed via the 242 next Via Address in the sequence of VIO. In normal operations, 243 the P-DAO is propagated along the chain of Via Routers from the 244 egress router of the path till the ingress one, which confirms the 245 installation to the root with a DAO-ACK message. Note that the 246 root may be the ingress and it may be the egress of the path, that 247 it can also be neither but it cannot be both. 249 The root is expected to use these mechanisms optimally and with 250 required parsimony to limit the state installed in the devices to fit 251 within their resources, but how the root figures the amount of 252 resources that is available in each device is out of scope for this 253 document. 255 In particular, the draft expects that the root has enough information 256 about the capability for each node to store a number of routes, which 257 can be discovered for instance using a Network Management System 258 (NMS) and/or the RPL routing extensions specified in "Routing for 259 Path Calculation in LLNs" [RFC6551]. 261 A route that is installed by a P-DAO is not necessarily installed 262 along the DODAG, though how the root and the optional PCE obtain the 263 additional topological information to compute other routes is out of 264 scope for this document 266 4.1. Non-storing Mode Projected DAO 268 As illustrated in Figure 2, the non-storing mode P-DAO enables the 269 root to install a source-routed path towards a target in any 270 particular router; with this path information the router can add a 271 source routed header reflecting the path to any packet for which the 272 current destination either is the said target or can be reached via 273 the target, for instance a loose source routed packet for which the 274 next loose hop is the target, or a packet for which the router has a 275 routing state to the final destination via the target. 277 ------+--------- 278 | Internet 279 | 280 +-----+ 281 | | Border Router 282 | | (RPL Root) 283 +-----+ | P ^ | 284 | | DAO | ACK | Loose 285 o o o o router V | | Source 286 o o o o o o o o o | P-DAO . Route 287 o o o o o o o o o o | Source . Path 288 o o o o o o o o o | Route . From 289 o o o o o o o o | Path . Root 290 o o o o o target V . To 291 o o o o | Desti- 292 o o o o | nation 293 destination V 295 LLN 297 Figure 2: Projecting a Non-Storing route 299 A router that receives a non-storing P-DAO installs a source routed 300 path towards each of the consecutive targets via a source route path 301 indicated in the following VIO. 303 When forwarding a packet to a destination for which the router 304 determines that routing happens via the target, the router inserts 305 the source routing header in the packet to reach the target. 307 In order to do so, the router encapsulates the packet with an IP in 308 IP header and a non-storing mode source routing header (SRH) 309 [RFC6554]. 311 In the uncompressed form the source of the packet would be self, the 312 destination would be the first Via Address in the VIO, and the SRH 313 would contain the list of the remaining Via Addresses and then the 314 target. 316 In practice, the router will normally use the "IPv6 over Low-Power 317 Wireless Personal Area Network (6LoWPAN) Paging Dispatch" [RFC8025] 318 to compress the RPL artifacts as indicated in the "6LoWPAN Routing 319 Header" [RFC8138] specification. In that case, the router indicates 320 self as encapsulator in an IP-in-IP 6LoRH Header, and places the list 321 of Via Addresses in the order of the VIO and then the target in the 322 SRH 6LoRH Header. 324 4.2. Storing-Mode Projected DAO 326 As illustrated in Figure 3, the storing mode P-DAO enables the root 327 to install a routing state towards a target in the routers along a 328 segment between an ingress and an egress router; this enables the 329 routers to forward along that segment any packet for which the next 330 loose hop is the said target, for instance a loose source routed 331 packet for which the next loose hop is the target, or a packet for 332 which the router has a routing state to the final destination via the 333 target. 335 ------+--------- 336 | Internet 337 | 338 +-----+ 339 | | Border Router 340 | | (RPL Root) 341 +-----+ | ^ | 342 | | DAO | ACK | 343 o o o o | | | 344 o o o o o o o o o | ^ | Projected . 345 o o o o o o o o o o | | DAO | Route . 346 o o o o o o o o o | ^ | . 347 o o o o o o o o v | DAO v . 348 o o LLN o o o | 349 o o o o o Loose Source Route Path | 350 o o o o From Root To Destination v 352 Figure 3: Projecting a route 354 Based on available topological, usage and capabilities node 355 information, the root or an associated PCE computes which segment 356 should be optimized and which relevant state should be installed in 357 which nodes. The algorithm is out of scope but it is envisaged that 358 the root could compute the ratio between the optimal path (existing 359 path not traversing the root, and the current path), the application 360 service level agreement (SLA) for specific flows that could benefit 361 from shorter paths, the energy wasted in the network, local 362 congestion on various links that would benefit from having flows 363 routed along alternate paths. 365 In order to install the relevant routing state along the segment 366 between an ingress and an egress routers, the root sends a unicast 367 P-DAO message to the egress router of the routing segment that must 368 be installed. The P-DAO message contains the ordered list of hops 369 along the segment as a direct sequence of Via Information options 370 that are preceded by one or more RPL Target options to which they 371 relate. Each Via Information option contains a Path Lifetime for 372 which the state is to be maintained. 374 The root sends the P-DAO directly to the egress node of the segment, 375 which In that P-DAO, the destination IP address matches the Via 376 Address in the last VIO. This is how the egress recognizes its role. 377 In a similar fashion, the ingress node recognizes its role as it 378 matches Via Address in the first VIO. 380 The egress node of the segment is the only node in the path that does 381 not install a route in response to the P-DAO; it is expected to be 382 already able to route to the target(s) on its own. It may either be 383 the target, or may have some existing information to reach the 384 target(s), such as a connected route or an already installed 385 projected route. If one of the targets cannot be located, the node 386 MUST answer to the root with a negative DAO-ACK listing the target(s) 387 that could not be located (suggested status 10 to be confirmed by 388 IANA). 390 If the egress node can reach all the targets, then it forwards the 391 P-DAO with unchanged content to its loose predecessor in the segment 392 as indicated in the list of Via Information options, and recursively 393 the message is propagated unchanged along the sequence of routers 394 indicated in the P-DAO, but in the reverse order, from egress to 395 ingress. 397 The address of the predecessor to be used as destination of the 398 propagated DAO message is found in the Via Information option the 399 precedes the one that contain the address of the propagating node, 400 which is used as source of the packet. 402 Upon receiving a propagated DAO, an intermediate router as well as 403 the ingress router install a route towards the DAO target(s) via its 404 successor in the P-DAO; the router locates the VIO that contains its 405 address, and uses as next hop the address found in the Via Address 406 field in the following VIO. The router MAY install additional routes 407 towards the addresses that are located in VIOs that are after the 408 next one, if any, but in case of a conflict or a lack of resource, a 409 route to a target installed by the root has precedence. 411 The process recurses till the P-DAO is propagated to ingress router 412 of the segment, which answers with a DAO-ACK to the root. 414 Also, the path indicated in a P-DAO may be loose, in which case the 415 reachability to the next hop has to be asserted. Each router along 416 the path indicated in a P-DAO is expected to be able to reach its 417 successor, either with a connected route (direct neighbor), or by 418 routing, for instance following a route installed previously by a DAO 419 or a P-DAO message. If that route is not connected then a recursive 420 lookup may take place at packet forwarding time to find the next hop 421 to reach the target(s). If it does not and cannot reach the next 422 router in the P-DAO, the router MUST answer to the root with a 423 negative DAO-ACK indicating the successor that is unreachable 424 (suggested status 11 to be confirmed by IANA). 426 A Path Lifetime of 0 in a Via Information option is used to clean up 427 the state. The P-DAO is forwarded as described above, but the DAO is 428 interpreted as a No-Path DAO and results in cleaning up existing 429 state as opposed to refreshing an existing one or installing a new 430 one. 432 5. Applications 434 5.1. Loose Source Routing in Non-storing Mode 436 A RPL implementation operating in a very constrained LLN typically 437 uses the Non-Storing Mode of Operation as represented in Figure 4. 438 In that mode, a RPL node indicates a parent-child relationship to the 439 root, using a Destination Advertisement Object (DAO) that is unicast 440 from the node directly to the root, and the root typically builds a 441 source routed path to a destination down the DODAG by recursively 442 concatenating this information. 444 ------+--------- 445 | Internet 446 | 447 +-----+ 448 | | Border Router 449 | | (RPL Root) 450 +-----+ ^ | | 451 | | DAO | ACK | 452 o o o o | | | Strict 453 o o o o o o o o o | | | Source 454 o o o o o o o o o o | | | Route 455 o o o o o o o o o | | | 456 o o o o o o o o | v v 457 o o o o 458 LLN 460 Figure 4: RPL non-storing mode of operation 462 Based on the parent-children relationships expressed in the non- 463 storing DAO messages,the root possesses topological information about 464 the whole network, though this information is limited to the 465 structure of the DODAG for which it is the destination. A packet 466 that is generated within the domain will always reach the root, which 467 can then apply a source routing information to reach the destination 468 if the destination is also in the DODAG. Similarly, a packet coming 469 from the outside of the domain for a destination that is expected to 470 be in a RPL domain reaches the root. 472 It results that the root, or then some associated centralized 473 computation engine such as a PCE, can determine the amount of packets 474 that reach a destination in the RPL domain, and thus the amount of 475 energy and bandwidth that is wasted for transmission, between itself 476 and the destination, as well as the risk of fragmentation, any 477 potential delays because of a paths longer than necessary (shorter 478 paths exist that would not traverse the root). 480 As a network gets deep, the size of the source routing header that 481 the root must add to all the downward packets becomes an issue for 482 nodes that are many hops away. In some use cases, a RPL network 483 forms long lines and a limited amount of well-targeted routing state 484 would allow to make the source routing operation loose as opposed to 485 strict, and save packet size. Limiting the packet size is directly 486 beneficial to the energy budget, but, mostly, it reduces the chances 487 of frame loss and/or packet fragmentation, which is highly 488 detrimental to the LLN operation. Because the capability to store a 489 routing state in every node is limited, the decision of which route 490 is installed where can only be optimized with a global knowledge of 491 the system, a knowledge that the root or an associated PCE may 492 possess by means that are outside of the scope of this specification. 494 This specification enables to store source-routed or storing mode 495 state in intermediate routers, which enables to limit the excursion 496 of the source route headers in deep networks. Once a P-DAO exchange 497 has taken place for a given target, if the root operates in non 498 storing mode, then it may elide the sequence of routers that is 499 installed in the network from its source route headers to destination 500 that are reachable via that target, and the source route headers 501 effectively become loose. 503 5.2. Transversal Routes in storing and non-storing modes 505 RPL is optimized for Point-to-Multipoint (P2MP), root to leaves and 506 Multipoint-to-Point (MP2P) leaves to root operations, whereby routes 507 are always installed along the RPL DODAG. Transversal Peer to Peer 508 (P2P) routes in a RPL network will generally suffer from some stretch 509 since routing between 2 peers always happens via a common parent, as 510 illustrated in Figure 5: 512 o in non-storing mode, all packets routed within the DODAG flow all 513 the way up to the root of the DODAG. If the destination is in the 514 same DODAG, the root must encapsulate the packet to place a 515 Routing Header that has the strict source route information down 516 the DODAG to the destination. This will be the case even if the 517 destination is relatively close to the source and the root is 518 relatively far off. 520 o In storing mode, unless the destination is a child of the source, 521 the packets will follow the default route up the DODAG as well. 522 If the destination is in the same DODAG, they will eventually 523 reach a common parent that has a route to the destination; at 524 worse, the common parent may also be the root. From that common 525 parent, the packet will follow a path down the DODAG that is 526 optimized for the Objective Function that was used to build the 527 DODAG. 529 ------+--------- 530 | Internet 531 | 532 +-----+ 533 | | Border Router 534 | | (RPL Root) 535 +-----+ 536 X 537 ^ v o o 538 ^ o o v o o o o o 539 ^ o o o v o o o o o 540 ^ o o v o o o o o 541 S o o o D o o o 542 o o o o 543 LLN 545 Figure 5: Routing Stretch between S and D via common parent X 547 It results that it is often beneficial to enable transversal P2P 548 routes, either if the RPL route presents a stretch from shortest 549 path, or if the new route is engineered with a different objective. 550 For that reason, earlier work at the IETF introduced the "Reactive 551 Discovery of Point-to-Point Routes in Low Power and Lossy Networks" 552 [RFC6997], which specifies a distributed method for establishing 553 optimized P2P routes. This draft proposes an alternate based on a 554 centralized route computation. 556 ------+--------- 557 | Internet 558 | 559 +-----+ 560 | | Border Router 561 | | (RPL Root) 562 +-----+ 563 | 564 o o o o 565 o o o o o o o o o 566 o o o o o o o o o o 567 o o o o o o o o o 568 S>>A>>>B>>C>>>D o o o 569 o o o o 570 LLN 572 Figure 6: Projected Transversal Route 574 This specification enables to store source-routed or storing mode 575 state in intermediate routers, which enables to limit the stretch of 576 a P2P route and maintain the characteristics within a given SLA. An 577 example of service using this mechanism oculd be a control loop that 578 would be installed in a network that uses classical RPL for 579 asynchronous data collection. In that case, the P2P path may be 580 installed in a different RPL Instance, with a different objective 581 function. 583 6. RPL Instances 585 It must be noted that RPL has a concept of instance but does not have 586 a concept of an administrative distance, which exists in certain 587 proprietary implementations to sort out conflicts between multiple 588 sources of routing information. This draft conforms the instance 589 model as follows: 591 o If the PCE needs to influence a particular instance to add better 592 routes in conformance with the routing objectives in that 593 instance, it may do so. When the PCE modifies an existing 594 instance then the added routes must not create a loop in that 595 instance. This is achieved by always preferring a route obtained 596 from the PCE over a route that is learned via RPL. 598 o If the PCE installs a more specific (say, Traffic Engineered) 599 route between a particular pair of nodes then it SHOULD use a 600 Local Instance from the ingress node of that path. A packet 601 associated with that instance will be routed along that path and 602 MUST NOT be placed over a Global Instance again. A packet that is 603 placed on a Global Instance may be injected in the Local Instance 604 based on node policy and the Local Instance paramenters. 606 In all cases, the path is indicated by a new Via Information option, 607 and the flow is similar to the flow used to obtain loose source 608 routing. 610 7. Security Considerations 612 This draft uses messages that are already present in RPL [RFC6550] 613 with optional secured versions. The same secured versions may be 614 used with this draft, and whatever security is deployed for a given 615 network also applies to the flows in this draft. 617 8. IANA Considerations 619 This document extends the IANA registry created by RFC 6550 for RPL 620 Control Codes as follows: 622 +------+-------------+---------------+ 623 | Code | Description | Reference | 624 +------+-------------+---------------+ 625 | 0x0A | Via | This document | 626 +------+-------------+---------------+ 628 RPL Control Codes 630 This document is updating the registry created by RFC 6550 for the 631 RPL 3-bit Mode of Operation (MOP) as follows: 633 +----------+------------------------------------------+-------------+ 634 | MOP | Description | Reference | 635 | value | | | 636 +----------+------------------------------------------+-------------+ 637 | 5 | Non-Storing mode of operation with | This | 638 | | Projected routes | document | 639 | | | | 640 | 6 | Storing mode of operation with Projected | This | 641 | | routes | document | 642 +----------+------------------------------------------+-------------+ 644 DIO Mode of operation 646 9. Acknowledgments 648 The authors wish to acknowledge JP Vasseur and Patrick Wetterwald for 649 their contributions to the ideas developed here. 651 10. References 653 10.1. Normative References 655 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 656 Requirement Levels", BCP 14, RFC 2119, 657 DOI 10.17487/RFC2119, March 1997, 658 . 660 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 661 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 662 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 663 Low-Power and Lossy Networks", RFC 6550, 664 DOI 10.17487/RFC6550, March 2012, 665 . 667 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 668 and D. Barthel, "Routing Metrics Used for Path Calculation 669 in Low-Power and Lossy Networks", RFC 6551, 670 DOI 10.17487/RFC6551, March 2012, 671 . 673 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 674 Routing Header for Source Routes with the Routing Protocol 675 for Low-Power and Lossy Networks (RPL)", RFC 6554, 676 DOI 10.17487/RFC6554, March 2012, 677 . 679 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 680 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 681 RFC 8025, DOI 10.17487/RFC8025, November 2016, 682 . 684 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 685 "IPv6 over Low-Power Wireless Personal Area Network 686 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 687 April 2017, . 689 10.2. Informative References 691 [I-D.ietf-6tisch-architecture] 692 Thubert, P., "An Architecture for IPv6 over the TSCH mode 693 of IEEE 802.15.4", draft-ietf-6tisch-architecture-13 (work 694 in progress), November 2017. 696 [I-D.ietf-detnet-architecture] 697 Finn, N., Thubert, P., Varga, B., and J. Farkas, 698 "Deterministic Networking Architecture", draft-ietf- 699 detnet-architecture-04 (work in progress), October 2017. 701 [PCE] IETF, "Path Computation Element", 702 . 704 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 705 J. Martocci, "Reactive Discovery of Point-to-Point Routes 706 in Low-Power and Lossy Networks", RFC 6997, 707 DOI 10.17487/RFC6997, August 2013, 708 . 710 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 711 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 712 2014, . 714 Appendix A. Examples 716 A.1. Using storing mode P-DAO in non-storing mode MOP 718 In non-storing mode, the DAG root maintains the knowledge of the 719 whole DODAG topology, so when both the source and the destination of 720 a packet are in the DODAG, the root can determine the common parent 721 that would have been used in storing mode, and thus the list of nodes 722 in the path between the common parent and the destination. For 723 instance in the diagram shown in Figure 7, if the source is node 41 724 and the destination is node 52, then the common parent is node 22. 726 ------+--------- 727 | Internet 728 | 729 +-----+ 730 | | Border Router 731 | | (RPL Root) 732 +-----+ 733 | \ \____ 734 / \ \ 735 o 11 o 12 o 13 736 / | / \ 737 o 22 o 23 o 24 o 25 738 / \ | \ \ 739 o 31 o 32 o o o 35 740 / / | \ | \ 741 o 41 o 42 o o o 45 o 46 742 | | | | \ | 743 o 51 o 52 o 53 o o 55 o 56 745 LLN 747 Figure 7: Example DODAG forming a logical tree topology 749 With this draft, the root can install a storing mode routing states 750 along a segment that is either from itself to the destination, or 751 from one or more common parents for a particular source/destination 752 pair towards that destination (in this particular example, this would 753 be the segment made of nodes 22, 32, 42). 755 In the example below, say that there is a lot of traffic to nodes 55 756 and 56 and the root decides to reduce the size of routing headers to 757 those destinations. The root can first send a DAO to node 45 758 indicating target 55 and a Via segment (35, 45), as well as another 759 DAO to node 46 indicating target 56 and a Via segment (35, 46). This 760 will save one entry in the routing header on both sides. The root 761 may then send a DAO to node 35 indicating targets 55 and 56 a Via 762 segment (13, 24, 35) to fully optimize that path. 764 Alternatively, the root may send a DAO to node 45 indicating target 765 55 and a Via segment (13, 24, 35, 45) and then a DAO to node 46 766 indicating target 56 and a Via segment (13, 24, 35, 46), indicating 767 the same DAO Sequence. 769 A.2. Projecting a storing-mode transversal route 771 In this example, say that a PCE determines that a path must be 772 installed between node S and node D via routers A, B and C, in order 773 to serve the needs of a particular application. 775 The root sends a P-DAO with a target option indicating the 776 destination D and a sequence Via Information option, one for S, which 777 is the ingress router of the segment, one for A and then for B, which 778 are an intermediate routers, and one for C, which is the egress 779 router. 781 ------+--------- 782 | Internet 783 | 784 +-----+ 785 | | Border Router 786 | | (RPL Root) 787 +-----+ 788 | Projected DAO message to C 789 o | o o 790 o o o | o o o o o 791 o o o | o o o o o o 792 o o V o o o o o o 793 S A B C D o o o 794 o o o o 795 LLN 797 Figure 8: Projected DAO from root 799 Upon reception of the P-DAO, C validates that it can reach D, e.g. 800 using IPv6 Neighbor Discovery, and if so, propagates the P-DAO 801 unchanged to B. 803 B checks that it can reach C and of so, installs a route towards D 804 via C. Then it propagates the P-DAO to A. 806 The process recurses till the P-DAO reaches S, the ingress of the 807 segment, which installs a route to D via A and sends a DAO-ACK to the 808 root. 810 ------+--------- 811 | Internet 812 | 813 +-----+ 814 | | Border Router 815 | | (RPL Root) 816 +-----+ 817 ^ Projected DAO-ACK from S 818 / o o o 819 / o o o o o o o 820 | o o o o o o o o o 821 | o o o o o o o o 822 S A B C D o o o 823 o o o o 824 LLN 826 Figure 9: Projected DAO-ACK to root 828 As a result, a transversal route is installed that does not need to 829 follow the DODAG structure. 831 ------+--------- 832 | Internet 833 | 834 +-----+ 835 | | Border Router 836 | | (RPL Root) 837 +-----+ 838 | 839 o o o o 840 o o o o o o o o o 841 o o o o o o o o o o 842 o o o o o o o o o 843 S>>A>>>B>>C>>>D o o o 844 o o o o 845 LLN 847 Figure 10: Projected Transversal Route 849 Authors' Addresses 850 Pascal Thubert (editor) 851 Cisco Systems 852 Village d'Entreprises Green Side 853 400, Avenue de Roumanille 854 Batiment T3 855 Biot - Sophia Antipolis 06410 856 FRANCE 858 Phone: +33 4 97 23 26 34 859 Email: pthubert@cisco.com 861 Rahul Arvind Jadhav (editor) 862 Huawei Tech 863 Kundalahalli Village, Whitefield, 864 Bangalore, Karnataka 560037 865 India 867 Phone: +91-080-49160700 868 Email: rahul.ietf@gmail.com 870 James Pylakutty 871 Cisco Systems 872 Cessna Business Park 873 Kadubeesanahalli 874 Marathalli ORR 875 Bangalore, Karnataka 560087 876 INDIA 878 Phone: +91 80 4426 4140 879 Email: mundenma@cisco.com